Will water go uphill into my grey tank?

Roktman

Member
Hey Guys, I’m building out a 7x7x12 v-nose cargo trailer into an Rv,good for campgrounds and especially off grid,SO ive got a small indoor shower and I’m going to install a grey water tank underneath, so the gray water tank will be a couple bays away so I’ll have to go beneath the 2 x 4 metal joists and back up slightly into the side of the graywater tank, i’ll just be using something like an inch and a quarter maybe even a semi flexible pipe, so I guess the question is where it goes up will that act as sort of a trap? Will the water have enough pressure to go into the tank or just slosh around in there, I’ve heard of these HEPVO traps ,a straight piece of pipe about eight or 10 inches long with internal elements that act as a trap it seems pretty successful, so I guess I’m just interested if the water will have enough pressure to climb 2 to 3 inches to get into the tank , what do you know ? Thanks guys
 

Ozarker

Pontoon Admiral
Not really understanding "go beneath joist".....

Yes, in a tank without baffles water will "slosh" around, that's not an issue with small tanks, water shifting shouldn't cause the trailer to turn over.

As long as the drain is higher than any rise in the pipe it should drain, but you could have water trapped in the line, best to put the drain above the tank.
 

simple

Adventurer
Water will always find a level equilibrium. As long as the input to the drain pipe is higher than the tank It will drain into the tank. How well it drains depends on the height difference between the shower drain opening and the top of the tank. In this case It sounds like you wont have much pressure for a strong flow and sediment may build up in the low spot of the drain.

I think you may want to have the water enter the grey tank at the top of the tank to keep sediment from building up in the "trap portion of the drain". I'd consider cutting through one of the floor crossmembers to get a straight sloping shot for the pipe running to the tank.
 

HaveeBear

New member
As plh noted, it will not go up. You will need pressure (forced or column of water - like your sink trap) to "push" the water into the gray tank, but you will have water left in the trap. Could also:
- drop the gray tank a couple of inches so water flows
- raise the shower floor a bit and create a drain trap (like your sink)
- pass drain through your metal joists
--- just thoughts. Good luck!
 

Peter_n_Margaret

Adventurer
If the shower basin is higher than the access to the tank it can syphon and flow into the tank.
A smaller pipe often works better than a larger one in this circumstance.
To improve the rate, enter the grey water tank as low down as possible and ensure that there is a generous vent at the top of the tank to let the air out. If the air can not get out, the water can not get in.
Filling from the bottom also stops any smells coming back up the pipe.
Cheers,
Peter
OKA196 motorhome
 

Roktman

Member
If the shower basin is higher than the access to the tank it can syphon and flow into the tank.
A smaller pipe often works better than a larger one in this circumstance.
To improve the rate, enter the grey water tank as low down as possible and ensure that there is a generous vent at the top of the tank to let the air out. If the air can not get out, the water can not get in.
Filling from the bottom also stops any smells coming back up the pipe.
Cheers,
Peter
OKA196 motorhome
Peter_n_Margaret, good info, thanks for taking the time
 

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